Field of the Invention
The present invention is related to allocating up to date shared resources and more particularly to selecting an optimal time for applying pending patches and updates to virtual machine images for satisfying resource requests and instantiating virtual machines with minimal delay and disruption.
Background Description
Acquiring, managing and maintaining Information Technology (IT) is a major budgetary concern for any modern organization. Moreover, since organizations seldom use local physical hardware (e.g., mainframe servers) at full capacity, frequently, some capacity is wasted. To reduce IT infrastructure costs and waste, instead of acquiring physical hardware, organizations are increasingly consolidating workload on shared hardware, using virtual machines (VMs) hosted on provider servers or computers. Ideally, each VM appears as an independent computer (e.g., a virtual processor, memory and disk space) running, for example, an operating system (OS) and a software stack with one or more active software elements (e.g., applications or other software).
As with any stand-alone computer, setting up a VM from scratch takes some measurable time. For example, provisioning a VM from scratch may involve allocating shared hardware for the VM and then, opening the OS and installing the software stack on the VM. So for efficiency, rather than repeatedly setting up VMs from scratch, providers are capturing the state of allocated virtual hardware and configured software in a file representation or virtual machine.
A minimum VM image is a file representation of a configured virtual machine and/or the virtual machine device(s). A VM image may further include all installed software components, i.e., the OS and software stack. Normally, each image is packaged with metadata describing corresponding hardware and software requirements in a virtual resource template (VRT or template). Each template includes at least one, and can include more than one, image. Since the number of potential VM images is unlimited, the provider selects a set of VM images and stores the images in a library of such images, for more efficiently provisioning virtual machines. Thereafter a virtualizer server loads VM image library image(s) to instantiate and run the respective virtual machine(s), and customizes the loaded image(s) for specific request requirements.
As with any state of the art computer system, virtual machines require updates or patches, e.g., to fix bugs, patch security weaknesses or patch software features. Updating or patching a virtual machine requires updating or patching the VM image, either to the VM image in the image library or individually patching the image each time it is instantiated. Patching the image individually, as a VM is being provisioned, limits potential wide ranging complications from the patch, but requires repeatedly patching/updating with no guarantee that of a successful patch for every instance, e.g., occasionally the patch may break the configuration. However, it may be relatively simple to recover from the broken configuration by re-provisioning the same VM without the patch. While patching an image library VM image may eliminate the patching and re-patching each VM, it affects every subsequently provisioned VM. Consequently deciding whether, when and how to patch the image library image is much more complex and risky.
Thus, there is a need for minimizing the time and resources required to patch VM images and VM instances, as well, and more particularly, there is a need for determining an optimum time for applying outstanding software patches or image updates without inadvertently applying updates that break existing image applications, damage software dependencies, or otherwise render customer applications completely unusable on the updated image.